The majority of eukaryotic mRNAs contain a tract of A residues at the end. These polyA-tails are not encoded in the DNA. Rather, they are added to the pre-mRNA "post-transcriptionally" (after transcription). The end of pre-mRNA is cut by a specific enzyme

The serine/threonine protein phosphatase 2A catalytic subunit alpha (PP2A, also known as A0132), is an isoform of the catalytic subunit of the serine/threonine phosphatase (PP2) and belongs to the PPP family of protein phosphatases, PP1 subfamily.